I have a 04 YZ450. It was bought from Canada so it is FIM regulated so it had that cone tail pipe, not the US model. I say that because I think the jetting is different. I have switched to a GYT-R muffler and am NOT running the spark arrester. I live in FL it is 90 degrees and 0 sea level. After I switched the muffler my head pipe will glow red right away in idle. I have not ridden it because this is BAD. I think the slow/pilot circuit is lean, but I cannot find any recommendations ANYWARE for this pipe. I am running the stock head pipe, if anyone has recommendations or a place to get them please let me know, thanks. Everything is stock, I have turned out the fuel screw to 3 turns.